The invention relates to a process for increasing the useful life of gas scavenging lances with porous graphite flush heads for non-ferrous metal melts. This especially concerns aluminum melts which are scavenged with argon.
The melt is purified, homogenized and degased by scavenging the metal melt with an inert gas. Scavenging is the last treatment phase before pouring the melt. The gas scavenging lance is manually or mechanically lowered in the crucible and the melt is scavenged for about five to ten minutes with an inert gas. The quality of the cast pieces is improved by the scavenging treatment since they obtain namely a dense structure and are free of porosity and, in addition, a good mold filling capacity is attained.
The gas scavenging lances have flush heads of porous materials. Since the lances are exposed to the high temperatures of the metal melts, their useful life is naturally short. This also applies to gas scavenging lances with flush heads of porous graphite although graphite is a temperature-stable material and the lance tube can also be made of graphite. The durability of graphite lances is, however, still limited since the graphite burns out after insertion in the melt as a result of the atmospheric oxygen.